GSB-050 Planetary Gearboxes can output up to 73 Nm (depends on ratio), and are suitable for servomotors up to 600W. Their output bearings allow for higher loads than GSA-050 gearboxes. This makes them suitable for helical rack&pinion systems up to module 2. They're maintenance free thanks to lifetime lubrication.
GSB-080 Planetary Gearboxes can output up to 168 Nm (depends on ratio), and are suitable for servomotors up to 2kW. Their reinforced tapered roller output bearings allow for very high radial loads. This makes them suitable for helical rack&pinion systems. Thanks to synthetic oil lubrication, the gears are better lubricated, better cooled, and run more smoothly. Under extreme conditions such as very high cyclic rates, GSA-080 gearboxes are the perfect option.